95 Saturn Overheating and the temp gage 3/4 vs 1/2 debate

Hello, my 95 SL2 A.T. starting to heat up in city traffic and the
Service Engine Soon light comes on. It used to go to the red and I had
it checked and the mechanic changed the temp sensor. The car, however,
still keeps heating to the point where the temp guage is 3/4 or very
near to the red area. I took it back to the mechanic and he said that
its "normal" behaviour.

I have also read the same thing here and other news groups and forums.
I do remember that upto a couple years ago before I started having all
these problems with my SL2, it ALWAYS stayed a notch below the 1/2
mark. The fan would come on and the temp never really went over the
"notch-before-the-1/2-mark".

Now my mechanic and almost everyone else tells me that its normal
(which may very well be). But why is it, that when I let the car do
the "normal" thing, ie; let it heat up to 3/4 or so the SES comes on
and the OBD gives me TRANSMISSION codes 22/23 etc..

If I do the heater/AC turn on dog-and-pony show, and keep the temp
between 1/4 and 1/2.. the SES never comes on, the car doesn't do the
abrupt shifting that it does when it gets to 3/4 temp guage and
everything seeems to work relatively smoothly.

Can someone tell me if there is a way to hard wire the fan and just be
done with this thing? I know I could prolly jumper the ends of the
temp sensor cable, but would that fry the computer if I do it for long
periods of time?

Hope someone can shed some light on this issue..